Bulb coating process



Oct. 19, 1954 5 JR 2,692,209"

BULB COATING PROCESS Filed April 29, 1953 V EATMOSPHLQ:

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VLowPezssue: A02 His tt Patented Oct. 19, 1954 BULB COATING PROCESSAugust E. Binder, Jr., Mentor-on-the-Lake, Ohio,

assignor to General Electric Company, a corporation of New YorkApplication April 29, 1953, Serial No. 351,985

3 Claims.

My invention relates in general to a method of interiorly coatingvitreous envelopes, such as lamp bulbs and the like, having a singleopening thereinto, and especially to a method of applying a luminescentmaterial to the inner surface of a selected portion of such envelopes.

Certain types of fluorescent lamps in general use at present employ aglass enclosure envelope or bulb having a bulbous portion provided withtubular extensions at its opposite ends one of which is closed off andthe other of which is open at its outer end to form the neck portion ofthe bulb, the inner surface of the bulbous portion of the bulb beingprovided with a coating of fluorescent material while the tubularextensions are left clear. For satisfactory appearance it is desirablethat the limiting or cut-01f edges of such fluorescent phosphor coatingsbe as straight as possible around the bulb and not of wavy or otherwiseirregular character. However, because the outer rim endof the neckportion of such bulbs normally is of irregular form with sharp andjagged edges such as preclude the use of a conventional pressure upflushmethod of applying the coating to the bulb wall by reason of thedifficulty of forming an airtight seal with such irregular edges, theformation of phosphor coatings with more or less straight cut-off edgesheretofore has been a difiicult and inconvenient operation to perform,the method previously in use having been to first coat the entire innersurface of the bulb with the phosphor material and to then remove thecoating from the tubular extensions of the bulb by a hand operation suchas by brushing or wiping.

It is an object of my invention, therefore, to

provide an improved method of applying a coating to a selected area ofthe inner surface of a lamp envelope or other hollow article having asingle opening thereinto, which method is easy and convenient to performand requires a minimum expenditure of time.

Another object of my invention is to provide an improved method ofapplying an internal fluorescent coating to the intermediate portiononly of a tubular lamp envelope having an opening at one end only,whereby the cut-off edges of the coating are formed substantiallystraight.

According to one aspect of the invention, a coating of fluorescentmaterial is first applied to the inner wall of the lamp envelopeextending inwardly from the open neck end thereof to the desired levelfor the innermost cut-off edge of the coating, by suction of asuspension of the fluorescent coating material upwardly into theenvelope to the said level, immediately followed by washing of thefluorescent coating off the neck end portion of the envelope up to thedesired lower cut-ofi level for the coating while simultaneouslydirecting air through the envelope to rapidly dry the remaining coatingon the bulb wall before it has an opportunity to drain therefrom such aswould result in the formation of undesirably thin and non-uniformcoatings.

Further objects and advantages of my invention will appear from thefollowing description of a species thereof and from the accompanyingdrawing in which:

Fig. 1 is a vertical section through a lamp envelope and associatedapparatus employed to perform the first or coating application step ofthe method comprising my invention, and

Fig. 2 is a vertical section through the envelope and associatedapparatus employed to perform the second step of the method comprisingmy invention wherein the portion of the coating on the lower or necksection of the envelope is removed and the remainder of the coating onthe envelope is dried in place on the envelope wall.

The invention is herein described and illustrated with reference to theformation of an internal coating of fluorescent material on a selectedintermediate portion of the length of a tubular glass envelope or bulb iwhich is closed at one end but open at the other end, the particularbulb illustrated having an enlarged ovalshaped or bulbous center portion2 provided with cylindrical extensions 3 and 4 at its opposite ends, theextension 3 being open at its outer end and constituting the neckportion of the lamp envelope and the other extension 4 being closed oifat its outer end by an end closure wall 5. It should be understood,however, that the invention can be utilized to apply any coatingmaterial of the type which can be flushed onto the surface to be coated,and that it is applicable to the coating of envelopes of shapes otherthan tubular which have a single entrance opening thereinto.

To provide an internal fluorescent coating on an intermediate portion ofthe length of the bulb I, for instance on the bulbous portion 2 only, bythe method according to the invention, the 'portion of the inner bulbsurface extending from the open end 6 of the neck portion 3 inwardly tothe innermost cut-off line i desired for the final coating, is firstflush-coated with a layer 8 (Fig. 2) of fluorescent material by suctionof a suspension of a fluorescent material upwardly into the bulb whilethe latter is positioned with its open neck end down. For this purpose,the neck end 3 of the bulb is placed over a vertical suction tube 9extending upwardly from the bottom wall Ii) of a container I I filledwith the coating suspension I2 to be applied to the bulb wall, the bathof coating suspension I2 being exposed to atmospheric pressure. Thephosphor coating suspension: IZ-may be any of the .types customs. arilyemployed in fluorescent lamp manufacture for applying coatings offluorescent material to the walls of the lamp envelopes, suchphosphors-c suspensions usually comprising a fluorescent phosphor powdersuspended in a suitable binder such as nitrocellulosedissolvedina'suitablersola' vent or thinner such as butyl acetate-oramyl' I acetate, with or without naphtha, for instance. The verticalsuction tube 9 is openatitsupper. end and is joined at its lower end tothe bottom wall IQ of the container I I in a liquid-tight man: ner. Thebulb I is moved down over the vertical suction-tube 3 until the upperend I3 oithelatter. is located above the. innermost. or: upper-:cut-oih:level-SI for the coatingv anduntilthe lower neck end 3 of the bulbiscompletely submerged in-the-i coating :suspension bath I2 .asufficient distance to remain submerged when .part of" the -coatingsuspension I2 inthe fcontainer'. II is drawn up..- into the. bulb to.the .-desir.ed. upper cut-off level] for the-coating. The bulb maybeconveniently supported in place by-resting the end. closure wall 5 .ofits top extension 4 on .the upper end: I3 .of'i the-suctiontube- 9; thesaid tube-for such-pur v pose being of sufiicient height toiocate-the-open". neck end 30f the bulb up off -the bottorn wallzI ofthecontainer Ii so-as to. permit free flow of the coating suspension:,I2 fromitheacontainen. into the bulb'neck-3. The suction tube -9 comemunicates .at its lower end with -.a :conduit,'or pipe. I4 which is.adapted-tobetconnectedby 'a. valve I5: in the said conduit, either to asource;- of vacuum,.oralternatively to the atmosphere so as to vent thesuctiontube 9..- The upper end or rim I3.of.the suction tube 9is-suitably notched-.- as indicated at I6 -to provide passageways intereconnecting theninterior of, thertubeii with the interior. space of thebulb.

With the bulb I rested inposition .on. the top I3.,of. thesuctionxtubeil and. its lower neck "end v=. 3 immersedinthe coating.suspension. i2 lll'fl'lherz container. I I, as shown. in Fig. -.1,,-thevvalve -I5 is set so. asv to connect .the -,suction...tubea9 :to: thesource of vacuum. The .resulting suction: createdinthetube-Q and bulb Ithendrawsrthei coatingsuspension; I 2..in..the containeral I -up;,into athe, :junctionbetween the enlarged :bulbous pore, i

tion,,2 Qanduthe -.upper cylindrical; extensionzr 01 the.-.bu1b,..thevacuum; is I shut {Ofi by means .of thevalve I5 and the suctiontubecthen connected.- instead .to theatmosphere by the zvalve-so as to, ventthe tube 9 and the interior of the bulb,-.asa resultof. ,which thecolumn of coatingsuspen sion. in the. bulb recedes approximately to.:its original starting level equalized with that of thecoating-suspension I2 outside the bulb. It..will..f. beobvious thatbythe useof-the above-described. particularup-fiush coating operation therising; column..of;.coating. suspensionin the bulb will. produce. a.perfectly. smooth. and straight .upper. cut-ofiedge around the bulbdefining a planenormal .to the bulb. axis, if..care is. taken .to seethat the bulb-is supported on the suction tube 3 I 4 in true verticalposition during the coating application operation.

Immediately after the coating 8 has been thus flushed onto the interiorwall of the bulb I, the bulb is carefully lifted off the suction tube 9so as not to mar the coating deposited on the bulb wall, and the saidcoating 8 then rapidly dried and set in place-by the .passageaofgza lowvelocity air current through the bulb to thereby minimize the drainageof the wet coating downwardly along the bulb wall such as would causethe coating to..thin. outwith resulting formation of an undesirably thinand non-uniform coating. In addition,..vvherev theneck portion 3 of thebulb is to be also'leftclear or free of coating, the portion of thephosphor coating on the neck portion 3 of the bulb. I isv suitablyremoved.

In accordance with the invention, this phosphor coating removaloperation is preferably performed simultaneously with the air drying ofthe coating on the-bulbous portion} .of-i-the-e-bulb. Forsuch-.pur.pose-.-.the phosphor coated neckiend; portion: 3 of the bulb.I is. immersed. up to the: desired lowercut-ofi level;.-I'I ina bath 18;(Fig.;; 2) of, thinnermaterial suchlas customarily employed as asolvent. for the nitrocellulose or other, binder used in..phosphorcoatings, exampleseof which thinnerxmateria-l. have been. previously,mentioned, The, thinner. bath: l8 ris preferably contained in atoroidal-shaped container orcup: I9 intotheannular chamber ofawhichtheneck end 31of-thebu1blis inserted to .the. required; depth to veffectimmersion. of ,;the.-.pl 1osphor-.coat. ingon the. bulb neckup tothedesired lower.cute:- ofielevel .II. which;for;.the.;particular..type::of..'. lamp. illustrated,gis locatedapproximately et the: junction betweenthe enlarged-bulbous portion 2.and .the cylindrical neck portion. 3 .ofithe bulb. The-bulb I may ,besupportedrin -proper. position... relative to. the thinnerbath .I8' toeffect theede sired extent of immersion-of. the bulb neck there-" in byrestingthe bulbous portion .2 of the-bulb on::

the upper annular rim.or end 20 of the; con-;-- tainer I9.. The-thinnerbath-.lfi-rac-ts to imam tainin suspension and-thuswashthe phosphorcoating'ofi the:bu1b neck .upto the level thereof. immersed in thethinner bath .so-that when the bulb neck is subsequently removed fromthe thine. ner bath the. said portion-of the bulb neck-.yvill be. leftsubstantially clear, and the-:phosphon coah. ing 8 remaining on the.bulb. wallzwill bevformeda; witha smooth and straight lower.cut-ofiedged 11.1: around. the bulb. To maintaimthethinner bathe. I 8in .the.:container; .I 9 aILthe: desired-lowers..cut;-..-- oil level ITfor the coatings-and prevent -.it,-from.;. risingabove suchlevelbyreason of-the. tendency of. the, phosphor; coating-washedeoif theeyvalls"of... successive gbulbs to. increase.-.-.-.the volume of their thinner.bath- I 8,. the zcontai-ner I 9 ..-is.; provided; with. a suitableoverflow outlet-.orzspout-Z I.

During. the interval while. the-neck. end 3 OffthE-jn bulb I is immersedin the.thinnerbathbm lowe velocity air, which -:may- :be heated .if:desired; is discharged into then-interior. spacer-of the:.-bulb;.--

above thelevel of the thinner therein, preferably; intothe topregion ofthe: bulb within .thecylin-'-.-- drical .top extension 4 thereof fromrayerticalairi. f

the bulb, as indicated by the arrows in Fig. 2, where it comes incontact with and dries the phosphor coating 8 on the inner surface ofthe bulb wall. The air stream passes out of the bulb through the annularspace between the air inlet tube 22 and the wall 25 of the centralpassageway 23 in the toroidal container [9.

When the phosphor coating 8 on the bulb wall has been suificiently driedand set in place thereon, the bulb is withdrawn from the thinner bath Itin the container [9 to thereby complete the coating operation.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of applying a coating of powdered material to the innersurface of a selected portion of the length of an envelope having anopen-ended neck portion providing the only opening thereinto, whichmethod comprises inserting the envelope neck end down into a bathcomprising a suspension of the coating material exposed to atmosphericpressure to completely submerge the open end of the said envelope neckportion in the said suspension bath, withdrawing the air in saidenvelope from a region adjacent the top thereof to create a suctiontherein and draw the said coating suspension up into the envelope,venting the interior space of the envelope above the coating suspensiontherein to the atmosphere when the column of coating suspension attainsthe desired predetermined upper cut-off level for the coating, to causethe column of coating suspension in the envelope to recede therefrom,and immediately immersing the neck end portion of the envelope up to thedesired predetermined lower cut-ofi level for the coating in a thinnerfor the said coating suspension while simultaneously passing a lowvelocity air stream through the interior space of the envelope above thethinner therein to dry and set in place the coating deposited on theinner wall of the envelope.

2. The method as set forth in claim 1 wherein the said air stream isdirected downwardly through the envelope from the top region thereof.

3. The method of applying a coating of powdered material to the innersurface of a selected portion of the length of an envelope having anopen-ended neck portion providing the only opening into the envelope,which method comprises positioning the envelope neck end down over avertically extending tube with the upper end of the said tube locatedabove the desired upper cut-oil? line for the coating on the envelopeand the open neck end of the envelope completely submerged in a bathcomprising a suspension of the coating material, connecting the lowerend of the said tube to a source of vacuum to create a suction in thetube and envelope and draw the said coating suspension up into theenvelope, disconnecting the said tube from the vacuum source and ventingit to the atmosphere when the rising column of coating suspensionattains the said upper cut-off line for the coating, to cause the columnof coating suspension in the envelope to recede therefrom, and thenimmediately placing the neck end of the envelope over a vertical airoutlet tube upstanding from the bottom of a container filled with aliquid thinner for the said coating suspension and immersing the saidneck end of the envelope in the said thinner up to the desired lowercut-off line for the coating on the envelope while simultaneouslyintroducing a low velocity stream of air into the top region of theenvelope, through a vertical air inlet tube extending through the saidair outlet tube, to dry and set in place the coating deposited on theinner wall of the envelope.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,096,416 Weinhart Oct. 19, 1937 2,303,290 Michael Nov. 24,1942 2,318,060 Cortese May 4, 1943

1. THE METHOD OF APPLYING A COATING OF POWDERED MATERIAL TO THE INNERSURFACE OF A SELECTED PORTION OF THE LENGTH OF AN ENVELOPE HAVING ANOPEN-ENDED NECK PORTION PROVIDING THE ONLY OPENING THEREINTO, WHICHMETHOD COMPRISES INSERTING THE ENVELOPE NECK END DOWN INTO A BATHCOMPRISING A SUSPENSION OF THE COATING MATERIAL EXPOSED TO ATMOSPHERICPRESSURE TO COMPLETELY SUBMERGE THE OPEN END OF THE SAID ENVELOPE NECKPORTION IN THE SAID SUSPENSION BATH, WITHDRAWING THE AIR IN SAIDENVELOPE FROM A REGION ADJACENT THE TOP THEREOF TO CREATE A SUCTIONTHEREIN AND DRAW THE SAID COATING SUSPENSION UP INTO THE ENVELOPE,VENTING THE INTERIOR SPACE OF THE ENVELOPE ABOVE THE COATING SUSPENSIONTHEREIN TO THE ATMOSPHERE WHEN THE COLUMN OF COATING SUSPENSION ATTAINSTHE DESIRED PREDETERMINED UPPER CUT-OFF LEVEL FOR THE COATING, TO CAUSETHE COLUMN OF COATING SUSPENSION IN THE ENVELOPE TO RECEDE THEREFROM,AND IMMEDIATELY IMMERSING THE NECK END PORTION OF THE ENVELOPE UP TO THEDESIRED PREDETERMINED